Novel photographic products and processes for color diffusion transfer utilizing silver halide emulsions with specific proportions of average halide grain size

ABSTRACT

THE PRESENT INVENTION RELATES TO PHOTOGRAPHY AND, MORE PARTICULARLY, TO DIFFUSION TRANSFER PROCESS PHOTOGRAPHIC FILM UNITS WHICH COMPRISE A PHOTOSENSITIVE ELEMENT ADAPTED TO PROVIDE, BY DIFFUSING TRANSFER PHOTOGRAPHIC PROCESS, SELECTIVE DYE IMAGE RECORDATION OF INCIDENT ACTINIC RADIATION AS A FUNCTION OF THE POINT-TO-POINT DEGREE OF PHOTOSENSITIVE ELEMENT EXPOSURE, WHICH FILM UNIT INCLUDES A PLURALITY OF ESSENTIAL LAYERS INCLUDING A PHOTOSENSITIVE SILVER HALIDE LAYER, COMPRISING PHOTOSENSITIVE SILVER IODOCHLOROBROMIDE WHICH CONTAIN IN TERMS OF THE HALIDE THEREOF, BY WEIGHT, NOT SUBSTANTIALLY IN EXCESS OF ABOUT 5% IODIDE AND ABOUT 10% CHLORIDE WITH BROMIDE SUFFICIENT TO PROVIDE 100%, THE GRAINS OF THE LAYER PREFERABLY POSSESSING A MEAN PARTICLE SIZE WITHIN THE RANGE OF ABOUT 0.3 TO 3.0U, HAVING ASSOCIATED THEREWITH DYE IMAGE-FORMING MATERIAL WHICH IS DIFFUSIBLE DURING PROCESSING AS A FUNCTION OF THE POINT-TO-POINT DEGREE OF SILVER HALIDE LAYER EXPOSURE TO INCIDENT ACTINIC RADIATION AND A LAYER ADAPTED TO RECEIVE DYE IMAGE-FORMING MATERIAL DIFFUSING THERETO; AND TO SPECIFIC DIFFUSION TRANSFER PROCESSES EMPLOYING SUCH FILM UNITS.

w. J. TIMSON 3,697,271 S AND PROCESSES FOR COLOR DIFFUSION ER HALIDE EMULSIONS WITH SPECIFIC 5 OF AVERAGE HALIDE GRAIN SIZE Oct. 10, 1972 NOVEL PHOTOGRAPHIC PRODUCT TRANSFER UTILIZING SILV PROPORTION Filed April 16, 1971 B Sheets-Sheet 1 FIG.

INVENTOR. WILLIAM J. TIMSON BY amwmuzea,

ATTORNEYS Oct. 10, 1972 w. J. TIMSON 3,697,271

NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES FOR COLOR DIFFUSION TRANSFER UTILIZING SILVER HALIDE EMULSIONS WITH SPECIFIC PROPORTIONS OF AVERAGE HALIDE GRAIN SIZE Filed April 16, 1971 8 Sheets-Sheet 2 @Iwwn and m and W W2. M

ATTORNEYS W. J. TIMSON Oct. 10, 1972 3,597,271 UCTS AND PROCESSES FOR COLOR DIFFUSI NOVEL PHOTOGRAPHIC PROD TRANSFER UTILIZING SILVER HALIDE EMULSIONS WITH SPECIFIC PROPORTIONS OF AVERAGE HALIDE GRAIN SIZE 1971 Filed April 16,

8 Sheets-Sheet 3 for.

INVENTOR. WILLIAM J. TIMSON BY @MW YL rl/rui AT TORNEYS 3,697,211 DIFFUSION PECIFIC W. J. TIMSON Oct. 10, 1972 S AND PROCESSES FOR COLOR NOVEL PHOTOGRAPHIC PRODUCT TRANSFER UTILIZING SILVER HALIDE EMULSIONS WITH 5 PROPORTIONS OF AVERAGE HALIDE GRAIN SIZE -971 8 Sheets-Sheet 4 Filed April 16,

5:: @ENJESUZ .523 5036/ f m N INVENTOR. WILLIAM J. TIMSON BY I106 Wujid.

and W 772. and AT TOR N E Y5 3,697,271 DIFFUSION 5 AND PROCESSE PROPORTIONS OF AVERAGE HALIDE GRAIN SIZE Filed April 16, 1971 8 Sheets-Sheet 5 w w m .Cw2uo momma :0 Q (imam- MJSNBCI 31d WVS INVENTOR. WILLIAM J. TIMSON ATTORNEYS W. J. TIMSON Oct. 10, 1972 ,697,Z71 OR DIFFUSION H SPECIFIC ZE NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES FOR COL TRANSFER UTILIZING SILVER HALIDE EMULSIONS WIT PROPORTIONS OF AVERAGE HALIDE GRAIN SI Filed April 16,

8 Sheets-Sheet 6 AllSNBO 31d WVS INVENTOR. WILLIAM J. TIMSON and 39M 77%. Gym

ATTORNEYS Oct. 10, 1972 Filed April 16,

w. J. TIMSON 3,69

NOVEL PHOTOGRAPHIC PRODUCTS AND PROCESSES FOR COLOR DIFFUSION TRANSFER UTILIZING SILVER HALIDE EMULSIONS WITH SPECIFIC PROPORTIONS OF AVERAGE HALIDE GRAIN SIZE 1971 8 Sheets-$heet '7 I2s|2s z41 21212.0] fs 1 |.'e 29 2.7 as 23 I l l l I l l 1 l "'2 cu N (\1 AIISNBG B'IdWVS INVENTOR. WILLIAM J. TIMSON BY 25km a/nd m and mmm.

ATTORNEYS United States Patent U.S. Cl. 96-3 31 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to photography and, more particularly, to diffusion transfer process photographic film units which comprise a photosensitive element adapted to provide, by diffusion transfer photographic processing, selective dye image recordation of incident actinic radiation as a function of the point-to-point degree of photosensitive element exposure, which film unit includes a plurality of essential layers including a photosensitive silver halide layer, comprising photosensitive silver iodochlorobromide which contain in terms of the halide thereof, by weight, not substantially in excess of about 5% iodide and about chloride with bromide sufficient to provide 100%, the grains of the layer preferably possessing a mean particle size within the range of about 0.3 to 3.0 having associated therewith dye image-forming material which is diffusible during processing as a function of the point-to-point degree of silver halide layer exposure to incident actinic radiation and a layer adapted to receive dye image-forming material diffusing thereto; and to specified diffusion transfer processes employing such film units.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention is directed to providing new and improved diffusion transfer process photographic film units adapted to provide, as a function of the point-topoint degree of photoexposure, by diffusion transfer processing a dye transfer image.

(2) Description of prior art As disclosed in U.S. Pat. No. 3,415,644, a composite photosensitive structure, particularly adapted for reflection type photographic diffusion transfer color process employment, which comprises a plurality of essential layers including, in sequence, a dimensionally stable opaque layer; one or more silver halide emulsion layers having associated therewith dye image-providing material which is soluble and diffusible, in alkali, at a first pH, as a function of the point-to-point degree of its associated silver halide emulsions exposure to incident actinic radiation; a polymeric layer adapted to receive solubilized dye image-providing material diffusing thereto; a polymeric layer containing sufficient acidifying capacity to effect reduction of a processing composition from the first pH to a second pH at which the dye image-providing material is substantially nondiffusible; and a dimensionally stable transparent layer, may be exposed to incident actinic radiation and processed by interposing, intermediate the silver halide emulsion layer and the reception layer, and alkaline processing composition possessing the first pH and containing opacifying agent, which may reflect incident radiation, in a quantity sufficient to mask dye image-providing material associated with the silver halide emul- $1011.

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In a preferred embodiment, the composite photosensitive structure includes a rupturable container, retaining the alkaline processing composition having the first pH and opacifying agent, fixedly positioned extending transverse a leading edge of the composite structure in order to effect, upon application of compressive pressure to the container, discharge of the processing composition intermediate the opposed surfaces of the reception layer and the next adjacent silver halide emulsion.

The liquid processing composition, distributed intermediate the reception layer and the silver halide emulsion, permeates the silver halide emulsion layers of-the composite photosensitive structure to initiate development of the latent images contained therein resultant from photoexposure. As a consequence of the development of the latent images, dye image-providing material associated with each of the respective silver halide emulsion layers is individually mobilized as a function of the point-topoint degree of the respective silver halide emulsion layers photoexposure, resulting in imagewise distributions of mobile dye image-providing materials adapted to transfer, by diffusion, to the reception layer to provide the desired transfer dye image. Subsequent to substantial dye image formation in the reception layer, a sufficient portion of the ions of the alkaline processing composition transfers, by diffusion, to the polymeric neutralizing layer to effect reduction in the alkalinity of the composite film unit to the second pH at which dye image-providing material is substantially nonditt'usible, and further dye imageproviding material transfer is thereby substantially obviated.

The transfer dye image is viewed, as a reflection image, through the dimensionally stable transparent layer against the background provided by the opacifying agent, distributed as a component of the processing composition, intermediate the reception layer and next adjacent silver halide emulsion layer. The thus-formed opacifying stratum effectively masks residual dye image-providing material retained in association with the silver halide emulsion layer subsequent to processing.

In U.S. Pat. No. 3,415,646, the dimensionally stable layer of the film unit next adjacent the photosensitive silver halide layer or layers is disclosed to be transparent to incident actinic radiation and as disclosed in U.S. Pat. No. 3,415,645, in such instance the opacifying agent may be initially disposed in the film unit intermediate the reception layer and next adjacent silver halide layer.

As disclosed in the copending U.S. patent application Ser. No. 846,441 of Edwin H. Land, filed July 31, 1969, now U.S. Pat. No. 3,615,421, and the copending U.S. patent application Ser. No. 3,646 of Sheldon A. Buckler, filed Jan. 19, 1970, now abandoned, the opacifying component of the film unit may optionally be initially disposed as a preformed processing composition permeable layer, intermediate the reception layer and next adjacent silver halide layer in a concentration which prior to photoexposure is insufficient to prevent transmission therethrough of exposing actinic radiation and which, subsequent to processing, possesses an opacifying capacity effective to mask residual dye image-providing material retained associated with the film units silver halide emulsion layers, and in the copending U.S. patent application Ser. No. 43,742 of Edwin H. Land, filed June 5,

1970, now U.S. Pat. No. 3,647,435, the opacifying com-' opacifying component is disclosed to optionally comprise a light-absorbing reagent such as a dye which is present as an absorbing species at the first pH and which may be converted to a substantially non-absorbing species at the second pH, and in U.S. Pats. Nos. 3,473,925 and 3,573,042 and the copending U.S. patent application of Terry W. Milligan and Richard W. Young, Ser. No. 864,397, filed Oct. 7, 1969, now U.S. Pat. No. 3,576,626, opacifying and reflecting component, respectively, may be individually interposed intermediate the silver halide layer and reception layer'by selective distribution from a composite or a plurality of rupturable containers.

In U.S. Pat. No. 3,573,043, the polymeric neutralizing layer is disclosed to be optionally disposed intermediate the dimensionally stable opaque layer and next adjacent essential layer, i.e., next adjacent silver halide/dye imageproviding material component, to effect the designated modulation of film units environmental pH; the copending U.S. patent application Ser. No. 846,442 of Edwin H. Land, filed July 31, 1969, now U.S. Patent .No. 3,594,164; 43,741, now U.S. Pat. No. 3,647,434; distributed within the film unit to effect the modulation of the environmental pH, and U.S. Pat. No. 3,573,044 discloses the employment of processing composition solvent vapor transmissive dimensionally stable layers to effect process modulation of dye transfer as a function of solvent concentration.

Where desired, the film unit may also be constructed in accordance with the disclosure of the copending U.S. patent applications of Howard G. Rogers, Ser. No. 39,646, filed, May 22, 1970, now U.S. Pat. No. 3,594,165, and Ser. No. 39,666, filed May 22, 1970, now U.S. Pat. No. 3,594,164, to comprise a composite photosensitive structure including a transparent dimensionally stable layer carrying a reception layer, a processing composition permeable opaque layer and a photosensitive silver halide layer and the film unit may include a separate dimensionally stable sheet element adapted to be superposed on the surface of the photosensitive structure opposite the dimensionally stable layer and may further include means such as a rupturable container retaining processing composition for distribution of a procesing composition intermediate the sheet and photosensitive structure to effect processing. As further disclosed in the last-cited applications, in structures wherein the receptor is positioned next adjacent the transparent layer or the processing composition and/or the sheet is to be separated from the remainder of the film unit subsequent to processing, the

latter elements may optionally include opacifying com ponent.

As disclosed in copending U.S. patent application Ser. No. 3,645 of Edwin H. Land, filed Jan. 19, 1970, now U.S. Pat. No. 3,620,724, the dimensionally stable layer referred to may be opaque and in which instance the photosensitive silver halide layer is positioned next adjacent the opaque support layer and the opacifying component of the film units processing composition permeable opaque layer will be disposed in the unit in a concentration insufiicient to prevent transmission therethrough of exposing actinic radiation and which, subsequent to processing, possesses an opacifying capacity effective to mask residual dye image-providing material retained associated with the silver halide layer, and as disclosed in the copending U.S. patent application Ser. No. 43,741 of Edwin H. Land, filed June 5, 1970, now U.S. Pat. No. 3,647,434, the opacifying agent may be optionally formed in such film unit, in situ, during processing of the unit.

SUMMARY OF THE INVENTION The present invention is directed to a new and improved, preferably integral negative/positive, diffusion transfer process photographic film unit adapted to provide, by diffusion transfer processing, photographic color image reproduction as a function of exposure of such film unit to incident actinic radiation.

The film unit assemblage construction to be employed in the practice of the present invention preferably comprises a film unit of the general type set forth in aforementioned U.S. Pats. Nos. 3,415,644, 5 and -6; 3,473,925; 3,573,042, -3 and -4; and copending U.S. patent applications Ser. Nos. 786,352, abandoned and replaced by U.S. Pat. No. 3,647,437; 846,441, now U.S. Pat. 3,615,421; 846,442, now U.S. Pat. No. 3,576,625; 864,397, now U.S. Pat. No. 3,576,626; 3,645, now U.S. Pat. No. 3,620,724; 3,691, now abandoned; 39,646, now U.S. Pat. No. 3,594,165; 39,666, now U.S. Pat. No. 3,594,164; 43,741, now U.S. Pat. No. 3,647,434; 43,742, now U.S. Pat. No. 3,647,435; and 43,782, abandoned and replaced by U.S. Pat. No. 3,647,437; and in U.S. Pats. Nos. 2,983,606 and 3,345,163; and will include a photosensitive silver halide layer which comprises photosensitive silver iodochlorobromide grains which contain in terms of the halide thereof, by weight, not substantially in excess of about 5% iodide and about 10% chloride with bromide sufiicient to provide disposed in a photosensitive element which contains a plurality of layers including, in relative order, a dimensionally stable layer preferably opaque to incident actinic radiation; one or more photosensitive silver halide layers having associated therewith dye image-forming material which is processing composition difiusible as a function of the point-to-point degree of silver halide layer exposure to incident actinic radiation; a layer adapted to receive image-forming material diffusion thereto; a dimensionally stable layer transparent to incident actinic radiation; and means for interposing, intermediate the silver halide layers and the reception layer, opacifying agent and a processing a composition, and, in a particularly preferred embodiment, a processing composition possessing a first pH at which the dye image-forming material is diifusible during processing and means for modulating the pH of the film unit from the first pH to a second pH at which the dye imageforming material is substantially nondiffusible subsequent to substantial dye transfer image formation.

In accordance with a specifically preferred embodiment of the present invention, a film unit assemblage of the aforementioned general structural parameters will be adapted to be processed, subsequent to photoexposure, in the presence of actinic radiation and may be fabricated to employ, as means interposed intermediate the reception layer and next adjacent silver halide layer subsequent to photoexposure, an inorganic light-reflecting pigment dispersion containing reflecting pigment and at least one optical filter agent, at a pH about the pKa of the optical filter agent and at which pH the dye image-forming material is diffusible during procesing as a function of silver halide layer photoexposure, in a concentration in admixture effective to provide a barrier to transmission of actinic radiation therethrough, and the means for interposing the opacifying agent and the processing composition may comprise a rupturable container, retaining the opacifying agent disposed in the processing composition selected, fixedly positioned extending transverse a leading edge of the film unit and adapted, upon application of compressive pressure, to distribute its contents intermediate the reception layer and next adjacent silver halide layer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a photographic film unit embodying the invention;

FIGS. 2, 4 and 6 are diagrammatic enlarged crosssectional views of the film unit of FIG. 1, along section line 24-2, illustrating the association of elements during the three illustrated stages of the performance of a diffusion transfer process, for the production of a multicolor transfer image according to the invention, the thickness of the various materials being exaggered, and wherein FIG. 2 represents an exposure stage, FIG. 4 represents a processing stage and FIG. 6 represents a product of the process;

FIGS. 3, and 7 are diagrammatic, further enlarged cross-sectional views of the film unit of FIGS. 2., 4 and 6, along section lines 3-3, -55 and 77, respectively, further illustrating, in detail, the arrangement of layers comprising the photosensitive laminate during the three I DETAILED DESCRIPTION OF THE INVENTION As previously characterized, diffusion transfer photographic processing may be employed to provide a positive reflection dye image, as a direct function of actinic radiation incident on a film unit assemblage which unit is preferably constructed to comprise a plurality of sequential layers including a dimensionally stable layer most preferably opaque to incident radiation; a photosensitive silver halide layer having associated therewith dye image-forming material which is processing composition dilfusible at a selected first pH as a function of the point-to-point degree of silver halide layer photoexposure; a layer adapted to receive dye image-forming material diffusing thereto; a dimensionally stable layer transparent to incident radiation; means for interposing, intermediate the silver halide layer and the reception layer, opacifying agent and preferably an inorganic reflecting pigment dispersion containing at least one optical filter agent or dye in a concentration effective to provide, subsequent to selective photoexposure of the silver halide layer, protection of the silver halide layer from further exposure to actinic radiation incident on the dimensionally stable layer; and means for converting the pH of the film unit from the first pH to a second pH at which the dye imageforming material is substantially nondiffusible subsequent to substantial dye image-forming material diffusion to the reception layer.

'It now has been discovered, however, that improved photographic reproduction in color by diffusion transfer processing may be accomplished by employment of a diffusion transfer process film unit which comprises a plurality of layers including photosensitive layer comprising photosensitive silver iodochlorobromide grains which contain in terms of the halide proportion thereof, by weight, not substantially in excess of either about 5% iodide and about 10% chloride with bromide to make up 100% having associated therewith a dye image-providing material which is dilfusible, during processing of the unit, as a function of the point-to-point degree of the photosensitive layers exposure to incident actinic radiation, and a layer adapted to receive dye image-providing material diffusing thereto.

In a preferred embodiment of the present invention, the photosensitive silver iodochlorobromide grains comprising the photosensitive layer possess a mean grain size distribution within the range of about 0.3 to 3.0;t.

Employment of diffusion transfer color process film units possessing the defined photosensitive silver iodochlorobromide components has been discovered to provide markedly increased diffusion transfer processing temperature latitude; film unit storage stability; and more efficient and effective utilization of silver, dye imageproviding components and photographic adjuvants as, for example, sensitizing dye components of the film unit.

Specifically, the employment of the denoted silver iodochlorobromide component possessing the defined halide constitution has been unexpectedly found to reduce the induction period for development of photoexposed grains thereby enhancing the dye diffusion control aspects of the dye transfer process with its concomitant improvement in transfer dye image acuity and resolution, and, in multicolor dye transfer processes, improved dye image separation and segregation. In addition, for presently unknown reasons, narrow grain distributions possessing small mean grain diameters which, in accordance with the present invention, exhibit higher sensitivity than that taught by the art as to be expected from such diameters, allow the utilization of the enhanced covering power of small grains and, accordingly, lower required concentration of photosensitive material per unit area to effectuate the same degree of dye transfer control and without the expected loss in sensitivity entailed in such employment. Enhanced dye transfer image control may thus be obtained per unit concentration of photosensitive silver halide.

It has been found that the advantages procured by means of the present invention are facilitated by maximizing restriction of the grain size distribution to the mean grain size selected to provide the results desired. Irrespective of such optimization, however, the photosensitivity response of the grains may be such as to provide a photoresponse gradient traditionally illustrated by the curve shape of the standard H & D type curve integrating processed silver image density at a function of film unit photoexposure.

It will be recognized that the employment of silver iodochlorobromide grain dispersions possessing maximally limited crystal size distribution and the last-mentioned photoresponse characteristics may be readily prepared in a plurality of expeditious manners, including the simple procedure which comprises the blending of dispersions possessing substantially homogeneous or uniform crystal size distributions where the silver halide crystal component of the dispersions forming the ultimate blend possesses differential electromagnetic radiation sensitivity.

In a particularly preferred embodiment of the present invention, about 75% and more preferably about of the photosensitive silver iodochlorobromide grains possess a substantially uniform grain size within the stated range of about 0.3 to 3.0a, and most preferably the substantially uniform silver iodochlorobromide grains are withiniabout 10% of the selected grain size, i.e., about 0.3:10% to 3.0- :l0%

Specifically, the employment of the silver halide grain size distribution denoted specifically facilitates the avoidance of the presence as a component of the photosensitive silver halide layer of a substantial proportion or number of grains possessing a diameter 3-0fl, which grains possess, as a function of surface area, a proclivity for formation of undesired fog, which proclivity increases as a direct function of increase in processing temperature, with the concomitant results of less efficient and effective utilization of a selected silver halide concentration per unit weight, degradation of image recordation acuity and corresponding dye transfer image construction. Conversely, the presence of a substantial number of grains possessing a diameter about 0.3 is also avoided, such grains having been found to exhibit relatively low effective sensitivity to exposure radiation, thus also resultant in less efficient utilization of silver halide to provide dye transfer image formation as a function of the film unit's exposure to actinic radiation.

Recognizing the although efficient utilization of silver halide in terms of its active species film unit coverage requirement decreases the excess quantities of silver halide, dye image-providing material and photographic adjuvants necessary to factor out inefiicient silver halide grain performance, most importantly control of the imagewise generation of and transfer of dye image-providing material is most accurately accomplished employing a silver halide grain distribution the sum total grains of which are active to individually contribute to selective generation and transfer of the image-providing components.

The preferred silver iodochlorobromide type photosensitive layers employed for the fabrication of the photographic film unit, may be prepared by reacting a watersoluble silver salt, such as silver nitrate, with at least one water soluble halide, such as ammonium, potassium or sodium chloride, together with corresponding iodide and bromide, in an aqueous solution of a peptizing agent such as colloidal gelatin solution; digesting the dispersion at an elevated temperature, to provide increased crystal growth; washing the resultant dispersion to remove undesirable reaction products and residual water-soluble salts, for example, employing the preferred gelatin matrix material, by chilling the dispersion, noodling the set dispersion, and washing the noodles with cold water, or, alternatively, employing any of the various flocc systems, or procedures, adapted to effect removal of undesired components, for example, the procedures described in US. Pats. Nos. 2,614,928; 2,614,929; 2,728,662, and the like; afterripening the dispersion at an elevated temperature in combination with the addition of gelatin or such other polymeric material as may be desired and various adjuncts, for example, chemical sensitizing agents of US. Pats. Nos. 1,574,944; 1,623,499; 2,401,689; 2,597,856; 2,597,915; 2,487,850; 2,518,698; 2,521,926; and the like; all according to the traditional procedures of the art, as described in Neblette, C. B., Photography, Its Materials and Processes, 6th Ed., 19-62.

Optical sensitization of the emulsions silver iodochlorobromide crystals may be accomplished by contact of the emulsion composition with an effective concentration of the selected optical sensitizing dyes dissolved in an appropriate dispersing solvent such as methanol, ethanol, acetone, water, and the like; all according to the traditional procedures of the art, as described in Hammer, F. M., The Cyanine Dyes and Related Compounds.

Additional optional additives, such as coating aids, hardeners, viscosity-increasing agents, stabilizers, preservatives, and the like, for example, those set forth hereinafter, also may be incorporated in the emulsion formulation, according to the conventional procedures known in the photographic emulsion manufacturing art.

As the binder for the photoresponsive material, the aforementioned gelatin may be, in whole or in part, replaced with some other natural and/or synthetic processing composition permeable polymeric material such as albumin; casein; or zein or resins such as cellulose derivative, as described in US. Pats. Nos. 2,322,085 and 2,541,- 474; vinyl polymeric suchas described in an extensive multiplicity of readily available US. and foreign patents or the photoresponsive material may be present substantially free of interstitial binding agent as described in US. Pats. Nos. 2,945,771; 3,145,566; 3,142,567; Newman, Comment on Non-Gelatin Film, B.J.O.P., 434, Sept. 15, 1961; and Belgian Pats. Nos. 642,557 and 642,558.

As previously mentioned, photosensitive silver iodochlorobromide emulsions possessing the preformed grain size distribution may be readily obtained by a plurality of conventional emulsion manufacturing procedures known to those skilled in the art, including procedures and apparatus particularly adapted to provide restricted and substantially homogeneous or uniform grain size distributions; see, for example, the processes and apparatus disclosed in US. Pats. Nos. 3,326,641 and 3,415,650, each of which is specifically hereby incorporated herein by reference.

One procedure particularly useful for the production of one preferred gelatino silver iodochlorobromide emulsion possessing a predetermined narrow grain size distribution comprises the formulation, in the manner peviously detailed of a silver iodochlorobromide emulsion containing in order of about 2% iodide and about 5% chloride by initially forming the emulsion, separating from the formulation undesired reaction products, and afterripening the resultant silver iodochlorobromide emulsion in combination with the selected auxiliary sensitizing, speed increasing, etc., adjuncts elected.

Specifically, the specified emulsion may be readily formulated by a conventional double jet addition, over a peri- 0d of one day, at a rate of 100 cc. per hour per jet, one jet delivering a solution comprising 3 M silver nitrate, in distilled water, at room temperature, the second jet delivering a solution comprising 3 M alkali halide (e.g. potassium) possessing 5% bromide, 5% i 5% chloride, 2.58: 2.5% iodide to equal in distilled water, at room temperature, to a 5% solution of gelatin in distilled Water, at room temperature, preadjusted to pH 6 with 5% sodium hydroxide. The resultant silver iodochlorobromide emulsion is held subsequent to formulation for the period of time required to provide the selected silver halide grain size distribution and separated from the reaction mixture, i.e., the supernatant liquid and washed with chilled distilled water until the wash water exhibits a conductivity of about 300 to 500 ,umhos/cm, the volume adjusted with distilled water for the addition of 20 gms. of gelatin per 1000 cc. of emulsion, and the emulsion then afterripening for 3 hours at a temperature of 60 C. and a pH of 5.5.

A plurality of the procedures which exist in the art, including those of the last-cited US. patents and application, employ mechanical particle classifier apparatus and techniques adapted to differentially separate materials of varying densities and materials of the same density and varying mass, which are, accordingly, particularly adapted to classify silver iodochlorobromide grains into desired distribution ranges and, at the election of the operator, provide further concentration or dilution of emulsion fluid volume specifically including counter-current centrifugal exchange devices; conventional mechanical centrifugation devices and procedures; in process centrifugal force field extraction employing hydrocyclone devices and procedures, etc.; positive sedimentation devices and procedures; and the like.

In preferred embodiments of the present invention, thephotosensitive silver iodochlorobromide emulsions employed will be emulsions adapted to provide a Diffusion Transfer Process Exposure Index about 50, which Index indicates the correct exposure rating of a diffusion transfer color process at which an exposure meter, calibrated to the ASA Exposure Index, must be set in order that it give correct exposure data for producing color transfer prints of satisfactorily high quality. The Diffusion Transfer Process Exposure Index is based on a characteristic H & D curve relating original exposure of the photosensitive silver iodochlorobromide emulsion to the respective curve densities forming the resultant transfer image. Thus, the Diffusion Transfer Exposure Index is based on the exposure to which the photosensitive silver iodochlorobromide emulsion, for use in color diffusion transfer processes, must be subjected in order to obtain an acceptable color transfer image by that process and is a direct guide to the exposure setting to be entered in a camera in order to obtain proper exposure of the filim unit.

In accordance with the present invention, it has also been discovered that excellent diffusion transfer dye image characteristic curve shape control, i.e., control of the transfer image characteristics represented graphically by the curve integrating dye density of the transfer image as a function of the log exposure of the photosensitive silver halide layer, may be obtained by utilization of a photosensitive silver halide layer which comprises a blend of differentially photosensitive silver halide dispersions at least one of the dispersions comprising the silver iodochlorobromide dispersions described above in admixture, for example; with a silver chlorobromide, -bromide, -iodobromide or -iodochlorobromide dispersion or dispersions, which blend preferably may possess a mean particle size within the previously denoted range of about 0.3 to 3.0,u.

Specifically, it has been discovered that upon blending the aforementioned differentially sensitive silver halide dispersions, the characteristic curve of the dye transfer image resultant from employment of the blend assumes the shoulder, i.e., low photosensitive silver halide layer photoexposure region, speed, i.e., relative measurement defined as a value representing the reciprocal of the exposure required to produce a predetermined result, of the fastest silver halide dispersion and the toe, i.e., high photosensitive layer photoexposure region, speed of the slowest silver halide dispersion, thus increasing theex posure latitude range and lowering the resultant slope or gamma of the curve.

There is thus provided the capacity for controlled formulation of photosensitive layers exhibiting a selectively extended range of predetermined gammas or contrasts and exposure latitudes or dynamic ranges, i.e., the relative measurement of the range of exposure from which a useful dye transfer image may be derived; the instant invention thereby providing the capability of a high maximum density, low minimum density and extended dynamic range dye diffusion transfer imaging system and thus adapted to more advantageously reproduce, as dye transfer image dilferences, the luminance differences existing in an object to be photographically reproduced, including optimization of the minimum useful exposures required to reproduce minimum differences existing in the shadow regions of the object to be reproduced by means of some minimum density differences in resultant dye transfer image conformation.

Referring to FIGS. 10 and 11, there is set forth in each figure a graph showing the characteristic curves of a dye transfer image determined by plotting the reflection density of the transfer image as a function of the log exposure of the photosensitive silver halide layer wherein Curve A in FIG. 10 and D in FIG. 11 represent the characteristic curves of dye transfer images employing photosensitive silver halide emulsions comprising a silver halide dispersion 95% of which silver halide possesses a particle size of 1.3;; :L-l%; Curves B and E represent the characteristic curves employing photosensitive silver halide emulsions comprising a silver halide dispersion 95% of which silver halide possesses a particle size of 0.9g i and wherein the photosensitive layers generating Curves A and D possess higher photographic speed or inherent sensitivity than those generating Curves B and E. Curves C and F denoted in FIGS. 10 and 11 represent the dye transfer image characteristic curves generated by 50:50 blends of the dispersions providing Curves A and 'B, and D and E, respectively.

Curves C and F in FIGS. 10 and 11 clearly exhibit the effect of blending the photosensitive silver halide dispersions generating Curves A and D with the less sensitive silver halide dispersions generating Curves B and E, and resultant Curves C and F illustrate that they are composites of Curves A and B, and D and B, respectively, possessing the shoulder speed of the more highly sensitive emulsion illustrated in Curves A and D and the toe speed of the less highly sensitive emulsion illustrated in Curves B and D and, with respect to Curve C, a composite gamma of 1.0 compound as compared with gammas of 2.9 and 2.7, respectively, for Curves A and B, and, with respect to Curve F, a composite gamma of 2.1 as compared with gammas of 2.9 and 2.7, respectively, for Curves D and E.

The results denoted illustrate graphically that desired dye transfer characteristic curve performance may be readibly obtained by the blending of silver halide dispersions possessing required toe and shoulder speeds to provide selected composite sensitometric results.

For the production of the data denoted above, film units were prepared by coating a polyester film base, in order, with a layer of the cyan dye developer 1,4-bis-(B-[hydroquinonyl-a-methyl]-ethyl-amino)-5,8 dihydroxy-anthraquinone dispersed in gelatin and coated at a coverage of about 70 mgs./ft. dye and about 70 mgs./ft. gelatin, a gelatino silver iodochlorobromide emulsion coated at a coverage of about 210 mgs./ft. silver and about 50 mgs./ ft. gelatin, which has been prepared in the manner denoted above and forming the predetermined narrow grain size emulsion, separating from the formulation undesired reaction products, and afterripening the resultant silver iodochlorobromide emulsion in combination with the selected auxiliary sensitizing, speed increasing, etc., adjuncts selected and, in the test structures, blending selected emulsion formulations.

A rupturable container, constructed as detailed hereinafter, containing an aqueous alkaline processing composition comprising:

, Percent Potassium hydroxide 12.0 Hydroxyethyl cellulose 3.8 N-phenethyl-u-picolinium bromide 3.5 Benzotriazole 3.5 Potassium thiosulfate 0.5 4'-methylphenyl hydroquinone 0.4 Lithium nitrate 0.5

was then mounted on the leading edge of each film unit such that, subsequent to exposure of each unit and upon application of compressive force to a container, its contents are distributed, upon rupture of the container distribution port, between the unit and the image-receptive layer of a contiguous dye transfer image-receiving element superposed coextensive the surface of the emulsion layer; the dye transfer image-receiving element prepared by coating, in order, with a polymeric acid layer comprising the partial butyl ester of a polyethylene/maleic anhydride copolymer 0.7 mil. thick; a polymeric spacer layer comprising a 6:4 mixture, by weight, of hydroxypropylcellulose and polyvinyl alcohol 0.3 mil. thick; and a polymeric image-receiving layer comprising a 2:1 mixture, by weight, of polyvinyl-alcohol and poly-4-vinyl pyridine 0.4 mil. thick and including about 20 mgs./ft. phenyl mercapto tetrazole.

In a preferred embodiment of the present invention, the means for interposing the processing composition selected intermediate the reception layer and the silver iodochlorobromide layer comprises a rupturable container retaining a processing composition comprising the solvent and pH concentrations required fixedly positioned and extending transverse a leading edge of the film unit to effect, upon application of compressive pressure, discharge of the processing composition intermediate the reception layer and the photosensitive silver iodochlorobromide layer next adjacent. In such embodiment the opacifying agent is preferably disposed within the processing composition, as retained in the rupturable container, for distribution as a component of such composition intermediate the reception and silver iodochlorobromide layers, subsequent to selective exposure of the film unit.

Multicolor images may be obtained using color imageforming components in the diffusion transfer process of the present invention by several techniques. One such technique contemplates obtaining multicolor transfer images utilizing, for example, dye developers as dye image-providing materials by employment of an integral multilayer photosensitive element, such as is disclosed in aforementioned US. Pat. No. 3,415,644 wherein at least two selectively sensitized photosensitive strata, superposed on a single support, are processed, simultaneously and without separation, with a single, common image-receiving layer. A suitable arrangement of this type comprises the opaque support carrying a red-sensitive silver iodochlorobromide stratum, a green-sensitive silver'iodochlorobromide stratum and a blue-sensitive silver iodochlorobromide stratum, said emulsions having associated therewith, respectively, for example, a cyan dye developer, a magenta dye developer and a yellow dye developer. The dye developer may be utilized in the silver iodochlorobromide stratum, for example, in the form of particles, or it may be employed as a layer behind the appropriate silver iodochlorobromide strata. Each set of silver iodochlorobromide strata and associated dye developer strata are disclosed to be optionally separated from other sets by suitable interlayers, for example, by a layer of gelatin or polyvinyl alcohol. In certain instances, it may be desirable to in-' corporate a yellow filter in front of the green-sensitive 1 1 emulsion and such yellow filter may be incorporated in an interlayer. However, where desirable, a yellow dye developer of the appropriate spectral characteristics and present in a state capable of functioning as a yellow filter may be employed. In such instances, a separate yellow filter may be omitted.

In a preferred embodiment of the present invention, the film unit is specifically adapted to provide for the production of a multicolor dye transfer image and the photosensitive laminate comprises, in order of essential layers, the dimensionally stable opaque layer; at least two selectively sensitized silver iodochlorobromide strata each having dye image-providing material of predetermined color associated therewith, for example, dye developers as detailed above, which are soluble and diifusible in processing composition as a function of the point-to-point degree of exposure of the respective associated silver iodochlorobromide stratum; a polymeric layer dyeable by the dye image-providing materials, and a dimensionally stable transparent layer.

In view of the fact that the preferred dye image-providing materials comprise dyes which are silver halide developing agents, as stated above, for purposes of simplicity and clarity, the present invention will be further described hereinafter in terms of such dyes, without limitation of the invention to the illustrative dyes denoted, and, in addition the photographic film unit structure will be detailed hereinafter employing the last-mentioned preferred structural embodiment, without limitation of the invention to the preferred structure denoted.

The dye developers, as noted above, are compounds which contain, in the same molecule, both the chromophoric system of a dye and also a silver halide developing function. By a silver halide developing function is meant a grouping adapted to develop exposed silver halide. A preferred silver halide development function is a hydroquinonyl group. Other suitable developing functions include ortho-dihydroxyphenyl and orthoand paraamino substituted hydroxyphenyl groups. In general, the development function includes a benzenoid developing function, that is, an aromatic developing group which forms quinonoid or quinone substances when oxidized.

The dye developers are preferably selected for their ability to provide colors that are useful in carrying out substractive color photography, that is, the previously mentioned cyan, magenta and yellow. The dye developers employed may be incorporated in the respective silver halide emulsion or, in the preferred embodiment, in a separate layer behind the respective silver halide stratum. Specifically, the dye developer may, for example, be in a coating or layer behind the respective silver halide stratum and such a layer of dye developer may be applied by use of a coating solution containing about 0.5 to 8%, by weight, of the respective dye developer distributed in a film-forming natural, or synthetic, polymer, for example,

gelatin, polyvinyl alcohol, and the like, adapted to be permeated by the chosen diffusion transfer fluid processing composition.

The silver iodochlorobromide strata comprising the multicolor photosensitive laminate preferably possess predominant spectral sensitivity to separate regions of the spectrum and each has associated therewith a dye which is a silver halide developing agent and is, most preferably, substantially soluble in the reduced form only at a first pH possessing, subsequent to processing, a spectral absorption range substantially complementary to the predominant sensitivity range of its associated emulsion.

In the preferred embodiment, each of the silver halide strata, and its associated dye, is separated from the remaining strata, and their associated dye, by separate alkaline solution permeable polymeric interlayers.

In such preferred embodiment of the invention, the silver halide strata comprises photosensitive silver iodochlorobromide dispersed in gelatin and are about 0.6 to 6 microns in thickness; the dye itself isdispersed in an aque- 12 ous alkaline solution polymeric binder, preferably gelatin, as a separate layer about 1 to 7 microns in thickness; the alkaline solution permeable polymeric interlayers, preferably gelatin, are about 1 to 5 mircons in thickness; the dyeable polymeric layer is transparent and about 0.25 to 0.4 mil in thickness; and each of the dimensionally stable opaque and transparent layers are alkaline solution impermeable, processing composition vapor permeable and about 2 to 6 mils in thickness. It will be specifically recognized that the relative dimensions recited above may be appropriately modified, in accordance with the desires of the operator, with respect to the specific product to be ultimately prepared.

Although in one embodiment of the present invention, the dimensionally stable layers employed in the practice of the invention may possess a vapor transmission rate of 1 or less gms./24 hrs/ inF/mil, in a preferred embodiment of the invention, the layers employed will possesss a vapor transmission rate for the selected processing composition solvent averaging not less than about 100 gms./24 hrs./ 100 in. /mil, most preferably in terms of the preferred solvent, water, a vapor transmission rate averagin in excess of about 300 gms. of water/24 hrs/100 infi/mil, and may advantageously comprise a microporous polymeric film possessing a pore distribution which does not unduly interfere with the dimensional stability of the layers or, where required, the optical characteristics of such layers. Such pore distribution may comprise, for example, an average pore diameter of from about 20 microns to about 100 microns and a pore volume of about 3% to about 7%.

In a particularly preferred embodiment of the present invention, the preferred solvent, water, may be employed in a weight/weight ratio of about 1:10 to 1:20 dye to water at a ratio of about 1:3 to 1:10 liquid permeable polymer to water and most preferably will be fabricated to comprise about 300 to 1300 mgs./ft. liquid permeable polymeric binder material, about 200 to 400 mgs./ft. dye and about 5000 mgs./ft. water.

The preferred dimensionally stable layers are designed so that there is no liquid flow through the layers while allowing the vapor of the processing composition solvent to pass by diffusion from the evaporating liquid body and the operational ei'ficiency of the film unit is directly dependent upon the nature and quality of the vapor permeable membrance characteristics of the layers selected. The vapor transmission characteristics desired are directed to maximization of the rate at which the required quantity of processing solvent is effectively evacuated from the film unit subsequent to substantial dye transfer image formation by diffusion transfer processing, commensurate with maintaining the liquid irnpermeability and dimensional stability characteristics of the layers. Thus, the layers should possess the maximum vapor transmission capacity which permits the passage of processing composition solvent vapor, and any gas dissolved therein, at its vapor pressure, without allowing passage of fluid processing composition. The layers employed in accordance with the present invention therefore should be as thin as possible ,for solvent vapor transmission efliciency yet suflicient strength to provide stability to and resist chemical and physical degradation of the film unit under conditions of use.

In the preferred embodiment of the present inventions film unit for the production of a multicolor transfer image, the respective silver halide/ dye developer units of the photo-sensitive element will be in the form of a trippack configuration which will ordinarily comprise a cyan dye developer/red-sensitive emulsion unit contiguous the dimensionally stable opaque layer, the yellow dye developer/blue-sensitive emulsion unit most distant from the opaque layer and the magenta dye developer/green-sensitive emulsion unit intermediate those units, recognizing that the relative order of such units may be varied in accordance with the desires of the operator.

Reference is now made to FIGS. 1 through 7 of the drawings wherein there is illustrated a preferred film unit of the present invention and wherein like numbers, appearing in the various figures, refer to like components.

As illustrated in the drawings, FIG. 1 sets forth a perspective view of the film unit, designated 10, and each of FIGS. 2 through 7 illustrate diagrammatic crosssectional views of film unit 10, along the stated section lines 2-2, 3--3, 55 and '7-7, during the various depicted stages in the performance of a photographic diffusion transfer process as detailed hereinafter.

Film unit comprises rupturable container 11, retaining, prior to processing, aqueous processing composition 12, and photosensitive laminate 13 including, in order, dimensionally stable opaque layer 14, preferably an actinic radiation-opaque flexible sheet material; cyan dye developer layer 15; red-sensitive silver iodochlorobromide emulsion layer 16 possessing the parameters denoted above; interlayer 17; magenta dye developer layer 18; green-sensitive silver iodochlorobromide emulsion layer 19 possessing the parameters denoted above; interlayer 20; yellow dye developer layer 21; blue-sensitive silver iodochlorobromide emulsion layer 22 possessing the parameters denoted above; auxiliary layer 23, which may contain an auxiliary silver halide developing agent; imagereceiving layer 24; spacer layer 25; neutralizing layer 26; and dimensionally stable transparent layer 27, preferably an actinic radiation transmissive flexible sheet material.

The structural integrity of laminate 13 may be maintained, at least in part, by the adhesive capacity exhibited between the various layers comprising the laminate at their opposed surfaces. However, the adhesive capacity exhibited at an interface intermediate image-receiving layer 24 and the silver iodochlorobromide emulsion layer next adjacent thereto, for example, image-receiving layer 24 and auxiliary layer 23 as illustrated in FIGS. 2 through 7, should be less than that exhibited at the interface between the opposed surfaces of the remainder of the layers forming the laminate, in order to facilitate distribution of processing solution 12 intermediate the stated imagereceiving layer 24 and the silver iodochlorobromide emulsion layer next adjacent thereto. The laminates structural integrity may also be enhanced or provided, in whole or in part, by providing a binding member extending around, for example, the edges of laminate 13, and maintaining the layers comprising the laminate intact, except at the interface between layers 23 and 24 during distribution of processing composition 12 intermediate those layers. As illustrated in the figures, the binding member may comprise a pressure-sensitive tape 28 securing and/or maintaining the layers of laminate 13 together at its respective edges. Tape 28 will also act to maintain processing solution 12 intermediate image-receiving layer 24 and the silver iodochlorobromide emulsion layer next adjacent thereto, upon application of compressive pressure to pod 11 and distribution of its contents intermediate the stated layers. Under such circumstances, binder tape 28 will act to prevent leakage of fluid processing composition from the film units laminate during and subsequent to photographic processing.

Rupturable container 11 may be of the type shown and described in any of US. Pats. Nos. 2,543,181; 2,634,886; 3653,732; 2,723,051; 3,056,492; 3,056,491; 3,152,515; and the like. In general, such containers will comprise a rectangular blank of fluidand air-impervious sheet material folded longitudinally upon itself to form two walls 29 which are sealed to one another along their longitudinal and end margins to form a cavity in which processing composition 12 is retained. The longitudinal marginal seal 30 is made weaker than the end seals 31 so as to become unsealed in response to the hydraulic pressure generated within the fluid contents 12 of the container by the application of compressive pressure to walls 29 of the container.

As illustrated in FIGS, 1, 2 and 3, container 11 is fixedly positioned and extends transverse a leading edge of photosensitive laminate 13 whereby to eflect unidirectional discharge of the containers contents 12 between image-receiving layer 24 and the stated layer next adjacent thereto, upon application of compressive force to container 11. Thus, container 11, as illustrated in FIG. 2 is fixedly positioned and extends transverse a leading edge of laminate 13 with its longitudinal marginal seal 30 directed toward the interface between image-receiving layer 24 and auxiliary layer 23. As shown in FIGS. 1, 2 and 4, container 11 is fixedly secured to laminate 13 by extension 32 of tape 28 extending over a portion of one wall of 29 of the container in combination with a separate retaining member such as illustrated 13s surface generally equal in area to about that covered by tape 28.

As illustrated in FIGS. 1, 2 and 4, extension flap 32 of tape 28 is preferably of such area and dimensions that upon, for example, manual separation of container 11 and tape 33, subsequent to distribution of processing composition 12, from the remainder of film unit 10, flap 32 may be folded over the edge of laminate 13, previously covered by tape 33, in order to facilitate maintenance of the laminates structural integrity, for example, during the flexation inevitable in storage and use of the processed film unit, and to provide a suitable mask or frame, for viewing the transfer image through the picture viewing area oftransparent layer 27.

The fluid contents of the container preferably comprise an aqueous alkaline solution having a pH and solvent concentration at which the dye developers are soluble and diifusible and contains inorganic light-reflecting pigment and at least one optical filter agent at a pH above the pKa of such agent in a quantity sufficient, upon distribution, effective to provide a layer exhibiting optical transmission density about 6.0 and optical reflection density about 1.0 to prevent exposure of photosensitive silver iodochlorobromide emulsion layers 16, 19 and 22 by actinic radiation incident on dimensionally stable transparent layer 27 during processing in the presence of such radiation and to afford immediate viewing of dye image formation in image-receiving layer 24 during and subsequent to dye transfer image formation. Accordingly, the film unit may be processed, subsequent to distribution of the composition, in the presence of such radiation, in view of the fact that the silver iodochlorobromide emulsion or emulsions of laminate are appropriately protected by incident radiation, at one major surface of the opaque processing composition and at the remaining major surface by the dimensionally stable opaque layer. If the illustrated binder tapes are also opaque, edge leakage of actinic radiation incident on the emulsion or emulsions will also be prevented.

The selected reflecting pigment should be one providing a background suitable for viewing the dye developer transfer image formed in the dyeable polymeric layer. In general, while substantially any reflecting agent may be employed, it is preferred that a reflecting agent be selected that will not interfere with the color integrity of the dye transfer image, as viewed by the observer, and, most preferably, an agent which is aesthetically pleasing to the viewer and does not provide a background noise signal degrading, or detracting from, the information content of the image. Particularly desirable reflecting agents will be those providing a white background, for viewing the transfer image, and specifically those conventionally employed to provide background for reflection photographic prints and, especially these agents possessing the optical properties desired for reflection of incident radiation.

As examples of reflecting pigments adapted for employment in the practice of the present invention, mention may be made of barium sulfate, zinc sulfide, titanium dioxide, barium stearate, silver flake, silicates, alumina,

15 zirconium oxide, zirconium acetyl acetate, sodium zirconium sulfate, kaolin, mica, and the like.

A particularly preferred reflecting agent comprises titanium dioxide due to its highly effective reflection properties. In general, in such preferred embodiment, based upon percent titanium dioxide (weight/volume) a processing composition containing about 1500 to 4000 rugs/ft. titanium dioxide dispersed in 100 cc. of water will provide a percent reflectance of about 85 to 90%. In the most preferred embodiments, the percent reflectance particularly desired will be in the order of about 85%.

In embodiments wherein the dispersion comprises a preformed layer positioned intermediate the reception layer and next adjacent silver iodochlorobromide layer, the pigment layer will be sufliciently transparent to allow transit of exposing radiation through the pigment layer and may comprise titanium dioxide reflecting agent possessing a particle size distribution averaging about 0.2,u. in diameter and preferably about 0.05; in diameter as initially present preceding exposure of the film unit, which preferred materials, upon contact with aqueous alkaline processing composition, preferably aggregate to provide particles possessing a diameter about 0.2,u in diameter and will be coated at a coverage of about 200 to 1000 mgs./ft. Specifically, the reflecting agent will be present in a quantity insufficient to prevent exposure of the emulsion layers by actinic radiation incident on the dimensionally stable transparent layer of the'film unit but in a concentration suflicient, subsequent to processing, to mask dye developer associated with the silver iodochlorobromide emulsion strata from the dyetransfer image. In the preferred construction of such embodiment, the pigment such as titanium dioxide will be initially present in a relatively small particle size to provide unexpectedly eflicient transit of radiation through the reflecting layer during exposure which upon contact with an alkaline processing composition and aggregation of the pigment particles provides eflicient light reflectivity and masking capacity subsequent to such aggregation.

In general, the reflecting agents to be employed are those which remain substantially immobile Within their respective compositions during and subsequent to photographic processing and particularly those which comprise insoluble and nondiffusible inorganic pigment dispersions within the layer in which they are disposed.

Wheredesired, reflecting agent pigment may thus be distributed in whole or in part within a processing composition permeable polymeric matrix such as gelatin and/ or any other such polymeric matrixes as are specifically denoted throughout the specification as suitable for employment as a matrix binder and may be distributed in one or more of the film unit layers which may be separated or contiguous, intermediate the image-receiving layer and next adjacent silver iodochlorobromide layer, provided that its distribution and concentration is effective to provide the denoted post processing masking function, and/or in whole or in part the reflecting agent may be ultimately disposed within the processing composition residuum located intermediate the image-receiving layer and next adjacent silver iodochlorobromide emulsion strata and associated dye image-forming material.

The optical filter agent selected should be one exhibiting, at a pH above its pKa, maximum spectral absorptionof radiation at the Wavelengths to which the film units photosensitive silver iodochlorobromide layer or layers are sensitive and should be substantially immobile or nondiifusible within the pigment dispersion, during performance of its radiation filtration function, in order to maintain and enhance the optical integrity of the dispersion as a radiation filter unit functioning in accordance with the present invention, and to prevent its diffusion into and localized concentration within the image-receiving layer thereby decreasing the efficiency of the reflecting pigment dispersion as a background against which image formation may be immediately viewed, during the initial stages in the diffusion transfer processing of the film unit, by filter agent absorption of dispersion reflected visible radiation prior to reduction in the environmental pH below the pKa of the agent. Commensurate with the spectral sensitivity range of the associated silver halide layer or layers, the optical filter agent selected may comprise one or more filter dyes possessing absorption complementary to such silver iodochlorobromide layers in order to provide elfective protection against physical fog providing radiation during processing. Recognizing that the filter agent absorption will derogate from image-viewing characteristics by contaminating reflecting pigment background, the selected agents should be those exhibiting major spectral absorption at the pH at which processing is effected and minimal absorption at a pH below that which obtains during transfer image formation. Accordingly, the selected optical filter agent or agents should possess a pKa below that of the processing pH and above that of the environmental pH subsequent to transfer image formation, and will be preferably selected for employment in the minimum concentration necessary to provide an optical transmission density about 6.0, at Wavelengths at which the silver iodochlorobromide layer is maximally responsive, and an optical reflection density about 1.0 at such Wavelengths.

As specified examples of such pH-sensitive optical filter agents adapted for employment in the practice of the present invention, reference is directed to the agents set forth in aforementioned copending US. patent application Ser. No. 43,782, filed June 5, 1970, now abandoned, incorporated herein by reference.

In general, preferred agents, both opacifying and filter, are those which remain immobile within their respective compositions during and subsequent to photographic processing and particularly those which comprise insoluble and nondiifusible materials.

As disclosed in the previously cited patents, the liquid processing composition referred to for effecting multicolor diffusion transfer processes comprises at least an aqueous solution of an alkaline material, for example, diethylamine, sodium hydroxide or sodium carbonate and the like, and preferably possessing a pH in excess of 12, and most preferably includes a viscosity-increasing compound constituting a film-forming material of the type which, when the composition is spread and dried, forms a relatively firm and relatively stable film. The preferred filmforming materials disclosed comprise high molecular weight polymers such as polymeric, water-soluble ethers which are inert to an alkaline solution such as, for example, a hydroxyethyl cellulose or sodium carboxymethyl cellulose. Additionally, film-forming materials or thickening agents whose ability to increase viscosity is substantially unaffected if left in solution for a long period of time are also disclosed to be capable of utilization. As stated, the film-forming material is preferably contained in the processing composition in such suitable quantities as to impart to the composition a viscosity in excess of cps. at a temperature of approximately 24 C. and preferably in the order of 100,000 cps. to 200,000 cps. at that temperature.

In the performance of a diffusion transfer multi-color process employing film unit 10, the unit is exposed to radiation, actinic to photosensitive laminate 13, incident on the laminates exposure surface, as illustrated in FIG. 3.

Subsequent to exposure, as illustrated by FIGS. 2 and 4, film unit '10 is processed by being passed through opposed suitably gapped rolls 35 in order to apply compressive pressure to frangible container 11 and to effect rupture of longitudinal seal 30 and distribution of alkaline processing composition 12, possessing inorganic lightreflecting pigment and optical filter agent at a pH above the pKa of the filter agent and a pH at which the cyan,

17 magenta and yellow dye developers are soluble and diffusible as a function of the point-to-point degree of exposure of red-sensitive silver iodochlorobromide emulsion layer 16, green-sensitive silver iodochlorobromide emulsion layer 19 and blue-sensitive silver iodochlorobromide emulsion layer 22, respectively, intermediate image-receiving layer 24 and auxiliary layer 23.

Alkaline processing composition 12 permeates emulsion layers 16, 19 and 22 to initiate development of the latent images contained in the respective emulsions. The cyan, magenta and yellow dye developers, of layers 15, 18 and 21, are immobilized, as a function of the development of their respective associated silver iodochlorobromide emulsions, preferably substantially as a result of their conversion from the reduced form to their relatively insoluble and nondiffusible oxidized form, thereby providing imagewise distributions of mobile, soluble and diifusible cyan, magenta and yellow dye developer, as a function of the point-to-point degree of their associated emulsions exposure. At least part of the imagewise distributions of mobile cyan, magenta and yellow dye developer transfers, by diffusion, to dyeable polymeric layer 24 to provide a multicolor dye transfer image to that layer which is viewable against the background provided by the reflecting pigment present in processing composition residuum 12 masking cyan, magenta and yellow dye developer remaining associated with blue-sensitive emulsion layer 22, green-sensitive emulsion layer 19 and red-sensitive emulsion layer 16. Subsequent to substantial transfer image formation, a sufficient portion of the ions comprising aqueous alkaline processing composition 12 transfer, by diffusion, through permeable polymeric reception layer 24, permeable spacer layer 25 to polymeric neutralizing layer 26 whereby the environmental pH of the system decreases as a function of neutralization to a pH at which the cyan, magenta and yellow dye developers, in the reduced form, are substantially nondiffusible to thereby provide a stable multicolor dye transfer image and discharge of the pH-sensitive optical filter agent by reduction of the pH substantially below the pKa of such agent to thereby provide maximum reflectivity in terms of the pigment concentration present.

The alkaline solution component of the processing composition, positioned intermediate the photosensitive element and the image-receiving layer, thus permeates the emulsions to initiate development of the latent images contained therein. The respective associated dy developers are mobilized in unexposed areas as a consequence of the development of the latent images. This mobilization is apparently, at least in part, due to a change in the solubility characteristics of dye developer upon oxidation and especially as regards its solubility in alkaline solutions. It may also be due in part to a tanning elfect on the emulsion by oxidized developing agent, and in part to a localized exhaustion of alkali as a result of development. In unexposed and partially exposed areas of the emulsions, the associated dye developer is diffusible and thus provides an imagewise distribution of unoxidized dye developer dissolved in the liquid processing composition, as a function of the point-to-point degree of exposure of the silver iodochlorobromide emulsion. At least part of this imagewise distribution of unoxidized dye developer is transferred, by imbibition, to a superposed image-receiving layer or element, said transfer substantially excluding oxidized dye developer. The image-receiving element receives a depthwise dilfusion, from the developed emulsion, of unoxidized dye developer without appreciably disturbing the imagewise distribution thereof to provide the reversed or positive color image of the developed image.

Subsequent to distribution of processing composition 12, container 11 may be manually dissociated from the remainder of the film unit, as described above, to provide the product illustrated in FIG. 6.

The present invention will be further illustrated and detailed in conjunction with the following illustrative constructions which set out representative embodiments and photographic utilization of the novel photographic film units of this invention, which, however, are not limited to the details therein set forth and are intended to be illustrative only.

Film units similar to that shown in the drawings may be prepared, for example, by coating, in succession, on a 5 mil opaque polyester film base, the following layers:

(1) A layer of the cyan dye developer dispersed in gelatin and coated at a coverage of about 98 mgs/ft. of dye and about 92 mgsJft. of gelatin;

(2) A red-sensitive gelatino-silver iodochlorobromide emulsion 95% of the silver iodochlorobromide grains of which possess a diameter of 1.8 1. i-10% coated at a coverage of about mgs./ft. of silver and about 27 mgs./ft. of gelatin;

(3) A layer of butyl acrylate/diacetone acrylamide/ styrene/methacrylic acid (60/30/4/6) and polyacrylamide coated in a ratio of about 29:1,- respectively, at a coverage of about 80 mgs./ft.

(4) A layer of the magenta dye developer and the auxiliary-developer 4'-methylphenyl hydroquinone dispersed in gelatin and coated at a coverage of about 81 mgs/ft. of dye, about 15 mgs./ft. of auxiliary developer and 54 mgs./ft. of gelatin;

(8) A blue-sensitive gelatino-silver iodochlorobromide emulsion 95% of the silver iodochlorobromide grains of which possess a diameter of 1.1g 210% coated at a coverage of about 65 mgs./ft. of silver and about 33 mgs./ft. of gelatin; and

(9) A layer of gelatin coated at a coverage of about 45 rugs/ft. of gelatin.

Then a transparent mil polyester film base may be coated, in succession, with the following illustrative layers:

(1) A 7:3 mixture, by weight, of polyethylene/maleic acid copolymer and polyvinyl alcohol at a coverage of about 1400 mgs./ft. to provide a polymeric acid layer;

(2) A graft copolymer of acrylamide and diacetone acrylamide on a polyvinyl" alcohol backbone in a molar ratio of 1:3.2:1 at a coverage of about 800 mgs./ft. to provide a polymeric spacer layer; and

(3) A 2:1 mixture, by Weight, of polyvinyl alcohol and poly-4-vinylpyridine, at a coverage of about 900 mgs./ ft. and including about 20 mgs./ft. phenyl mercapto tetrazole, to provide a polymeric image-receiving layer.

The two components thus prepared may then be taped together in laminate form, .at their respective edges, by means of a pressure-sensitive binding tape extending around, in contact with, and over the edges of the resultant laminate.

A rupturable container comprising an outer layer of lead foil and an inner liner or layer of polyvinyl chloride retaining an aqueous alkaline processing solution comprising:

may then be fixedly mounted on the leading edge of each of the laminates, by pressure-sensitive tapes interconnecting the respective containers and laminates, such that, upon application of compressive pressure to a container, its contents may be distributed, upon rupture of the containers marginal seal, between the polymericimage-receiving layer and next adjacent gelatin layer.

The photosensitive composite film units may be exposed through radiation incident on the transparent cellulose triacetate layer and processed by passage of the exposed film units through appropriate pressure-applying members, such as suitably gapped, opposed rolls, to efiect rupture of the container and distribution of its contents. Subsequent to processing, the multicolor dye 20 transfer image formation may be viewed through the transparent polyester layer against the titanium dioxide background provided by distribution of the pigment containing processing composition between layer 9 and the polymeric image-receiving layer. Multicolor dye trans fer image formation will be found to be substantially completed and exhibiting the required color brilliance, hues, saturation and isolation, within a period of approximately seconds.

[For purposes of illustrating the advantageous results achieved by reason of the present invention, film units, fabricated essentially as denoted above, were processed in the stated manner, at processing temperatures of and 40 F., in combination with appropriate control film units, of the same general structure, which specifically comprised conventional blue-, greenand red-sensitive gelatino silver iodobromide emulsions possessing random polydisperse particle size distributions.

Specifically, the film unit, both the control and test units, were exposed to a conventional step wedge to provide the graphic illustration of the characteristic curves of the respective dye transfer images, forming the multicolor dye positive images, set forth in FIGS. 8 and 9.

The detailed characteristic curves were determined by plotting the density of the respective images to red, green and blue light, as a function of the log exposure of the photosensitive element, wherein FIG. 8 represents the characteristic curves of test and control film units processed at 40 F. and FIG. 9 represents the characteristic curves of test and control film units processed at 100 F.

Curves A, B and C of FIGS. 8 and 9, respectively, represent the characteristic cyan, magenta and yellow transfer image dye curves (read to red, green and blue reflected light) of the test film units and Curves 'D, E and P, re spectively, represent the corresponding curves of the control film units.

As will be expressly noted from examination of the respective curves, the previously described significant improvement in dye transfer image control and processing temperature latitude is directly achieved by means of the present invention.

The gelatino silver iodochlorobromide emulsions employed will preferably possess the silver halide distribution gradient detailed hereinbefore and may be prepared as previously detailed and chemically sensitized, at about 56 0., pH 5 and pAg 9, by the addition of a sensitizing amount of a solution containing 0.1 gram of ammonium thiocyanate in 9.9 cc. of water and 1.2 cc. of a solution containing 0.097 gram of gold chloride in 9.9 cc. of water, and a 0.02% aqueous sodium thiosulfate solution. The resultant emulsions may then be appropriately sensitized spectrally by addition of aneifective concentration of one or more optical sensitizing dyes dispersed in an appropriate carrier solvent.

By addition of (A) 2.08 gms.

to the processing composition, image formation may be immediately viewed upon distribution of the processing composition by reason of the protection against incident radiation aiforded the photosensitive silver halide emulsion layers by the compositions optical transmission density of about 6.0 density units and against the titanium dioxides effective reflective background aiforded by reason of the composition possessing an optical reflection density about 1.0 density units.

The enhanced sensitivity per unit size exhibited by the silver iodochlorobromide emulsions of the present invention may be illustrated by the comparative data, set forth below in Table I, generated employing film units which may comprise, as the photosensitive element, a mil opaque polyester film base carrying, in order, a layer of the magenta dye developer 2 (p 3 hydroquinonylethyl] phenylazo) 4 isopropoxy-l-naphthol dispersed in gelatin and coated at a coverage of about 26 mgs./fm. dye and a gelatino-silver iodochlorobromide emulsion possessing a halide ratio, by weight, and particle size distribution, designated in Table I, coated at a coverage of about 78 mgs./ft. silver and, as the processing composition and the image-receiving element,

the composition and reception element denoted in the monochomatic construction denoted first above.

The gelatino-silver iodochlorobromide emulsion may be readily prepared by the addition of an aqueous silver nitrate solution to an aqueous solution comprising the appropriate mole percent potassium chloride, potassium iodide and ammonium bromide in gelatin and distilled water to provide the requisite silver iodochlorobromide emulsions possessing the halide ratios denoted in Tables I and H, set forth hereinafter. The gelatino-silver iodochlorobromide emulsion may then be separated from the reaction mixture by flocculation with ammonium sulfate, the supernatant liquid removed, and the fiocculate washed with chilled distilled water until the wash water exhibits a conductivity of about 500 ,umhos/cm, the emulsion volume adjusted by the addition of distilled water and gelatin, and the temperature raised to about 40 C. and the pH and p'Br adjusted to about 6 and 3,

respectively. The emulsion may then be afterripened to optimum speed and chemically sensitized in accordance with the procedure set forth in detail hereinafter.

Emulsions possessing the various halide ratios utilized to provide Tables I and II may thus be readily obtained by employment of the reactant halide concentration ratios desired, and the particle size selected by operational control of the respective emulsions afterripening temperature and duration.

Film units constructed essentially as denoted above and possessing the selected halide ratios and particle size distributions, were exposed to a conventional step wedge to provide the characteristic curve of the magenta dye trans-- fer images, upon processing in the previously described manner, providing the characteristic curve 0.6 speed measurements, i.e., the speed of a film unit measure on the characteristic curve at a transfer image dye density of 0.6, set forth in Table I below, integrated with the respective 50 and 84 percentile particle size distribution of the emulsions silver halide grains as measured employing a Zeiss TGZ-3 particle size analyzer.

TABLE I 1% iodide 2% iodide 4% iodide 0% chloride 0. 9471 Particle size (fifty percentile). 2. 04414 Particle size (eighty-four percentile). 1 2. 0.6 speed.

1% chloride. 0. 831 0. 742,44 0. 958 Particle size 1.398n 1. 3511:. 2. 361 (eighty-four percentile). 2.92 2.78 2.63 0.6 speed.

2% chloride... 0. 087p 0. 691p 0. 770 1 Particle size (fifty percentile). l.314 l.168 .t 1.382p Particle size (eighty-four percentile). 2.90 2.74 2.66 0.6 speed.

4% chloride..- 0. 793p 0. 720;; 0. 548p Particle size (fifty percentile) L2731L l.200;4 0. 967p Particle size (eighty-four percentile). 2.76 2.62 2.60 0.6 speed.

6% chloride... 0. 774p 0. 747 Particle size (fifty percentile). 1.243u 1. 350 Particle size (eighty-four percentile). 2.82 2.60 2.48 0.6 speed.

As will be noted from examination of the 0.6 speed measurements of the table in concert with the stated particle size distributions, 'when compared with the control silver iodobromide emulsion prepared in the same manner as the test silver iodochlorobromide emulsions, the emulsions of the present invention exhibit unexpectedly high sensitivity, at small particle size distributions, with the concomitant result of thus providing increased developed image silver covering power and its corollary of improved transfer image control, without sacrifice in the photorespouse characteritsics of the film unit.

Processing temperature latitude improvement is further established by comparative data which may be generated in the manner detailed immediately above employing a film unit which may comprise, as the photosensitive element, a 5 mil opaque polyester film base carrying, in order, a layer of the chromium complexed magenta dye developer denoted above dispersed in gelatin and coated at a coverage of about 50 mgs./ft. dye and about 50 mgs./ft. gelatin, and a gelatino-silver iodochlorobromide emulsion, prepared as denoted immediately above, containing the auxiliary silver halide developing agent 4'- methylphenylhydroquinone and coated at a coverage of about 4 mgs./ft. auxiliary developer and about 65 mgs./ ft. silver and, as the processing composition and the image-receiving element, the composition and reception element denoted in the trichromatic construction denoted above.

Film units, constructed essentially as denoted above, were exposed to a conventional step wedge to provide the characteristic curve of the magenta dye transfer images upon processing in the previously described manner, at processing temperatures of 100 and 40 F., the characteristics curve AO.6 speed shifts of the respective units, as a function of processing temperature and halide composition, set forth in Table II below.

TABLE II A 0.6 speed, processing temperature 'Test 40 F. 100 F.

Silver iodobromide emulsion control (2% iodide,

98% bromide) 0. 37 +0. 38

Silver iodochlorobromide emulsion (1% iodide,

1% chloride, 98% bromide) -0. 23 +0. 18 Silver doehlorobromide emulsion (1% iodide, 2%

chloride, 97% bromide) 0. 17 +0. 16 Silver iodochlorobromide emulsion (1% iodide, 4%

chloride, 95% bromide) 0. 18 0. 8 Silver iodochlorobromide emulsion (1% iodide, 6%

chloride, 93% bromide) 0. l9 0. 7

As will be noted from examination of the A0.6 speed figures set forth in Table II, the silver iodochlorobromide emulsions of the present invention when compared with the control silver iodobromide emulsion exhibit significantly increased processing temperature latitude, i.e., decrease in A0.6 speed over the stated range of processing temperatures.

The pH and solvent concentration of the alkaline processing solution initially employed will possess a pH above the pKa of the optical filter agents where the latter are employed, that is, the pH at which about 50% of the agents are present as the lesser absorbing species and about 50% are present as the greater absorbing species, preferably a pKa of about l1 and most preferably about 12 and a pH at which the dye developers employed are soluble and dilfusible. Although it has been found that the specific pH to be employed may be readily determined empirically for any dye developer and optical filter agent, or group of dye developers and filter agents, most particularly desirable dye developers are soluble at pHs above 9 and relatively insoluble at pHs below 9, in reduced form, and relatively insoluble at substantially any alkaline pH, in oxidized form, and the system can be readily balanced accordingly for such dye developers. In addition, although as previously noted, the processing composition, in the preferred embodiment, will include the stated" film-forming viscosity-increasing agent, or agents, to facilitate spreading of the composition and to provide maintenance of the spread composition as a struc turally stable layer of the laminate, subsequent to distribution, it is not necessary that such agent be employed as a component of the composition.

Neutralizing means, for example, a polymeric acid layer of the type discussed above may be incorporated, as stated, in the film unit of the present invention, to provide reduction of the alkalinity of the processing solution from a pH above the pKa of the optical filter agent selected at which the dyes are soluble to a pH below the pKa of theagent at which the dyes are substantially nondiffusible, in order to advantageously further stabilize and optimize reflectivity of the dye transfer image. In such instance, the neutralizing layer may comprise particulate acid reacting reagent disposed within the film unit or a polymeric acid layer, for example, a polymeric acid layer approximating 0.3 to 1.5 mils in thickness, positioned intermediate the transparent support and image-receiving layer, and/or the opaque support and next adjacent emulsion/ dye unit layer, and the film unit may also contain a polymeric spacer or barrier layer, for example, approximating 0.1 to 0.7 mil in thickness, next adjacent the polymeric acid layer, opposite the respective support layer, as previously described.

Specifically, the film units may employ the presence 24 of a polymeric acid layer such as, for example, of the type set forth in US. PatrNo. 3,362,819 which, most preferably, includes the presence of an inert timing or spacer layer intermediate the polymeric acid layer carried on a support and the image-receiving layer.

As set forth in the last-mentioned patent, the polymeric acid layer may comprise polymers which contain acidgroups, such as carboxylic acid and sulfonic acid groups, which are capable of forming salts with alkali metals, such as sodium, potassium etc., or with organic bases, particularly quaternary ammonium bases, such as tetramethyl ammonium hydroxide, or potentially acid-yielding groups, such as anhydrides or lactones, or other groups which are capable of reacting with bases to capture and retain them. The acid-reacting group is, of course, retained in the polymer layer. In the preferred embodiments disclosed, the polymer contains free carboxyl groups and the transfer processing composition employed contains a large concentration of sodium and/or potassium ions. The acid polymers stated to be most useful are characterized by containing free carboxyl groups, being insoluble in water in the free acid form, and by forming water-soluble sodium and/ or potassium salts. One may also employ polymers containing carboxylic acid anhydride groups, at least some of which preferably have been converted to free carboxyl groups prior to imbibition. While the most readily available polymeric acids are derivatives of cellulose or of vinyl polymers, polymeric acids from other classes of polymers may be used. As examples of specific polymeric acids set forth in the application, mention may be made of dibasic acid half-ester derivatives of cellulose which derivatives contain free carboxyl groups, e.g., cellulose acetate hydrogen phthalate, cellulose acetate hydrogen glutarate, cellulose acetate hydrogen succinate, ethyl cellulose hydrogen succinate,. ethyl cellulose acetate hydrogen succinate, cellulose acetate hydrogen succinate, hydrogen phthalate; ether and ester derivatives or cellulose modified with sulfoanhydrides, e.g., with ortho-sulfobenzoic anhydride; polystyrene sulfonic acid; carboxymethyl cellulose; polyvinyl hydrogen phthalate; polyvinyl acetate hydrogen phthalate; polyacrylic acid; acetals of polyvinyl alcohol with carboxy or sulfo substituted aldehydes, e.g., o-, m-, or p-benzaldehyde sulfonic acid or carboxylic acid; partial esters of ethylene/maleic anhydride copolymers; partial esters of methyl-vinyl ether/maleic anhydride copolymers; etc.

As previously noted, the pH of the processing composition preferably is of the order of at least 12 to 14 and the pKa of the selected optical filter agents will accordingly preferably be in the order of 13 or greater. The polymer layer is disclosed to contain at least sufiicient acid groups to effect a reduction in the pH of the image layer from a pH of about 12 to 14 to a pH of at least 11 or lower at the end of the imbibition period, and preferably to a pH of about 5 to 8 within a short time after imbibition, thus requiring, of course, that the action of the polymeric acid be accurately so controlled as not to interfere with either development of the negative or image transfer of unoxidized dye developers. For this reason, the pH of the image layer must be kept at a functional transfer level, for example, 12 to 14 until the dye image has been formed after which the pH is reduced very rapidly to a pH below that at which dye transfer may be accomplished, for example, at least about 11 and preferably about pH 9 to 10. Unoxidized dye developers containing hydroquinonyl developing radicals diffuse from the negative to the positive as the sodium or other alkali salt. The diffusion rate of such dye image-forming components thus is at least partly a function of the alkali concentration, and it is necessary that the pH of the image layer remain on the order of, for example, 12 to 14 until transfer of the necessary quantity of dye has been accomplished. The subsequent pH reduction, in addition to its desirable effect upon image light stability, serves a highly valuable photographic function by substantially terminating further dye transfer. 

